The present invention relates to copolymers comprising perfluoroalkyl groups and to a process for the production of these copolymers. The invention also relates to radiation-sensitive reproduction layers containing these copolymers as binders and to the use of these reproduction layers for waterless offset printing.
Other than in the customarily used offset-printing process, where differentiation between image areas and non-image areas during printing is effected by the simultaneous action of water or water-containing liquids, on the one hand, and printing ink, on the other hand, differentiation in waterless planographic printing, particularly offset printing, normally results from the fact that the ink-receptive, i.e., oleophilic, image areas and the ink-repellent, i.e., oleophobic, non-image areas (which are not moist with water) on a printing plate surface show different interactions with the printing ink. From the state of the art, the following publications are known.
U.S. Pat. No. 3,677,178 discloses a printing plate in which a support material comprising a metal, a plastic, or paper is coated with a layer of a hydrophobic and oleophobic silicone rubber and a radiation-sensitive reproduction layer, in the indicated or in the reverse order. As the radiation-sensitive compound, the reproduction layer contains ammonium dichromate, formaldehyde condensates of diphenylamine-4-diazonium salts, or polyvinyl cinnamate. In the printing process, the ink-receptive areas either comprise bared portions of the support material or portions of the reproduction layer which have been cured by irradiation.
In the printing plate according to U.S. Pat. No. 3,511,178 and U.S. Pat. No. 3,682,633, the support material is first coated with a radiation-sensitive reproduction layer and then with a coating having a lower release value (reduced adhesive interaction) with respect to printing inks than the support material. The last-mentioned coating either comprises a polysiloxane (silicone elastomer) or a fluorine-containing organic compound, for example, a homopolymer of the methacrylic acid ester of perfluorooctanol.
Further embodiments of printing plates for waterless offset-printing and of compounds which are suitable for use in printing plates of this kind are, for example, disclosed in the following publications:
U.S. Pat. No. 3,953,212 discloses a combination of a radiation-sensitive compound and a silicone rubber in one layer which is applied to one of the customary support materials. The printing plate according to German Auslegeschrift No. 24 22 428 (equivalent to British Patent No. 1,464,123) contains a photopolymerizable polysiloxane and a photosensitizer in a single layer.
In German Offenlegungsschrift No. 25 24 562 (equivalent to British Patent No. 1,501,128) radiation-sensitive coatings are described, which comprise an aromatic diazonium cation, an anion of a carboxylic acid or sulfonic acid containing perfluoroalkyl groups and, optionally, a polymeric organic binder. It is stated that these layers can be used for printing directly after irradiation, i.e., a developing step is not required.
The printing plates according to U.S. Pat. No. 4,087,584 comprise, in an oleophobic coating, a fluorine-containing homopolymer or copolymer having monomer units derived from acrylic or methacrylic acid esters containing perfluoroalkyl groups, or perfluoroalkanesulfonamido-alkyl groups. In copolymers, the proportion of the fluorine-containing monomer units exceeds 75 %. This oleophobic coating is either present directly on a support material and image areas are applied to the coating or it is present on top of an electrophotographically working reproduction layer. In the latter case, toner images are produced on the oleophobic coating.
U.S. Pat. No. 3,910,187 discloses various possibilities of producing printing plates for use in waterless offset printing by applying an intermediate or final layer to customary photopolymer printing plates (i.e., printing plates comprising a support material and a reproduction layer containing photopolymerizable compounds). These intermediate or final layers comprise perfluoroalkyl group-containing carboxylic acids, sulfonic acids, phosphonic acids and amines or polymers of perfluoroalkyl group-containing acrylic or methacrylic acid esters, maleic acid diesters, vinyl ethers, carboxylic acid vinyl esters, sulfonamido-allyl esters, and the like. The polymers are either prepared from the above-indicated monomers before application to the printing plates or are produced by photopolymerization directly on the printing plate.
According to published European Patent Application No. 0,037,094, it is possible to prepare radiation-sensitive polymers for, among other uses, as coatings for printing plates, which contain copolymers of (a) acrylic or methacrylic acid perfluoroalkyl esters and (b) acrylic or methacrylic acid azidobenzoyloxyalkyl esters. In addition to these copolymers, radiation-sensitive reproduction layers can also contain alkaline-developable organic binders and customary additives. After irradiation and development, a relief image is produced on the support material.
Published European Patent Application No. 0,040,841 describes radiation-sensitive polymers,
comprising copolymers of (a) monomers having perfluoroalkyl end groups and ethylenically unsaturated end groups and (b) monomers having radiation-sensitive groups and ethylenically unsaturated groups. The monomers mentioned under (a) include, for example, acrylic or methacrylic acid perfluoroalkyl esters and the monomers mentioned under (b) include, for example, methacrylic acid azidobenzoyloxyalkyl esters, acrylic acid cinnamoyloxyalkyl esters, methacrylic acid benzoylphenyl esters, or methacrylic acid cinnamoylphenyl esters.
From published European Patent Application No. 0,096,845 radiation-sensitive polymers are known which comprise copolymers of (a) acrylic or methacrylic acid-2-perfluoroalkoxy-2-fluoro-ethyl-1-esters or related compounds, (b) monomers containing radiation-sensitive groups and ethylenically unsaturated groups, and (c) optionally further fluorine-free copolymerizable vinyl monomers.
In the hitherto known reproduction layers for the production of printing plates used in waterless offset printing, organic solvents such as 2-butoxyethanol, ethylene glycol monoethyl ether, methylene chloride, dioxane, or hexafluoro-m-xylene, must frequency be used in the developing step. Because of this, expensive redistillation units and the like are required to enable an ecologically acceptable reclaiming of these solvents. Moreover, the synthesis of the starting components is often difficult (for example, requiring several stages), so that they are not at all or only to a minor degree suitable for large-scale industrial application. Reproduction layers which do not contain a binder and/or are not subjected to an additionally differentiating developing step after the irradiation thereof, generally do not yield relatively large print runs. Reproduction layers which include a binder and already contain a fluoroalkyl group-containing compound as the radiation-sensitive component, are not readily prepared, since it is often impossible or at least difficult to combine the customary binders with these compounds to form a homogeneously acting coating. The effects of a possible incompatibility of the two principal components of reproduction layers, i.e., the radiation-sensitive component and the binder component, frequently do not appear in the preparation of the coating composition, but are discovered only during or after drying of the layers, i.e., when the solvent or dispersing agent is removed.